For what it's worth, most of my experience over the last few years is that they don't do this, though exactly when they turn it off varies a bit from one flight to the next, even on the same carrier. I've watched movies all the way to the gate on Delta multiple times, though. Delta almost always seems to turn on the IFE prior to takeoff.
That said, after landing, often the flight attendants will start making announcements as soon as the aircraft has slowed to taxi speed. Most (all?) IFE systems I've encountered pause and lock out the IFE while announcements are in progress, so, in practice, it becomes difficult to catch much more of whatever you're watching after landing, due to the IFE system being locked out until they stop making announcements. Similarly, the IFE systems are generally locked out during pre-flight safety briefings (and often are used to deliver the briefings) during taxi-out.
One rather unfortunate consequence of the lock-out during announcements is that a lot of the flights I've encountered on multiple carriers play music or some such thing over the PA during boarding, which unnecessarily locks out the IFE systems. Similarly, international flights often make announcements in multiple languages and the IFE gets locked out for everyone for all of the repetitions.
